The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Substrate processing systems may be used to anneal, deposit and etch film on a substrate such as a semiconductor wafer. The substrate processing systems for deposition and etching typically include a processing chamber, a gas distribution device and a substrate support. During processing, the substrate is arranged on the substrate support. Different gas mixtures may be introduced into the processing chamber and radio frequency (RF) plasma may be used to activate chemical reactions.
Further scaling of transistors will require materials to replace silicon (Si) in transistor channels. Use of germanium (Ge) and silicon germanium (SiGe), particularly with strain, have been proposed for future generations of transistors. Growth of strained Ge or SiGe nanowires or nanowires that are several nanometers wide is a prerequisite for using these materials in FinFET and gate-all-around (GAA) devices. The Ge or SiGe nanowires need to be defect-free to ensure high carrier mobility in the channel.
There is a 4.2% lattice mismatch between Ge and Si. Therefore, direct epitaxial growth of Ge or SiGe on Si leads to a dislocation density of ˜108 cm−2, which causes degradation in device performance. Thick composition-graded Si1-xGex buffer layers can be used to decrease the dislocation density. However, these buffer layers have a thickness on the order of hundreds of nanometers, which is not consistent with scaling of transistors.
Aspect ratio trapping (ART) methods have been used to deposit materials in narrow trenches on silicon substrates. Dislocation defects originating at an interface between Si and Ge or SiGe are trapped in a bottom portion of a trench. Ideally, the top portion of the trench is defect free. In practice, however, the defects tend to propagate to a top surface of Ge or SiGe along the length direction of trenches.